Bacterial Morphology and physiology

Question 1

what is the difference between bacterial cells and mammalian cells?

Answer 1

bacterial cells = prokaryotes = no nucleus, cell wall, no cell organelles

eukaryotes = nucleus, no cell well, and contain cell organelles

Question 2

what are the features of a gram positive organism

Answer 2

gram - pos = have a thick layer of peptidoglycan surrounding the cell membrane and have low cell - wall lipid content

Question 3

what properties does a gram negative organism have?

Answer 3

they have a thin peptidoglycan layer and high cell-wall lipid content

Question 4

what reagents are used in a gram staining process?

Answer 4

1) crystal violet
2) iodine (fixes violet color)
3) alocohol - takes out violet color in gram negative organisms
4) neutral red - dyes the gram negative bacteria, and does not effect the gram positive

Question 5

why does alcohol have it’s effect on gram positive/negative organisms?

Answer 5

gram positive = have low lipid content and is therefore dehydrated by alcohol making it impermeable

gram negative = high lipid content which is extracted by alcohol to permeabilise the membrane= red color

Question 6

what sort of organism do we use a Ziehl-Neelson stain for?

Answer 6

mycobacteria

they are not stained using gram stain due to a high wax content in cell envelope

Question 7

You should know these

Question 8

Describe the bacterial cell structure

Answer 8

genome

cytoplasmic membrane

cell wall

outer membrane of gram - negative bacteria

capsules/slime layers

Question 9

What does cytoplasm contain?

Answer 9

composed of approx 80% water

contains enzymes that breakdown glucose and other carbon sources to provide energy - enxymes involved in cell wall synthesis

ribosomes - protein synthesis

genome - single tightly folded molecule of double stranded DNA - chromosomal DNA and also small circular extrachromasomal DNA - plasmid DNA

Question 10

what is the role of the cytoplasmic membrane?

Answer 10

composed primarily of lipids and proteins -

hyrdrophilic portion of lipid faces towards the aqueous environment

• acts as osmotic barrier -
• transports-
• site of energy production (electron transport chain)

Question 11

what is peptidoglycan?

Answer 11

primary component of the bacterial cell wall

prevents osmotic lysis

gram negative bacteria have one or two peptidoglycan layers

gram positive bacteria have many peptidoglycan layers

Question 12

what lies on the surface of gram-positive organisms?

Answer 12

they have wall teichoic acid and lipoteichoic acid strains on the surface

Question 13

what does the gram negative bacterial cell wall/envelope consist of

Answer 13

gram negative cells have cell membrane, then thin layer of peptidoglycan, then outer cell membrane

-

Question 14

what is the function of the gram-negative cell envelope?

Answer 14

bacterial cell adhesion

resistance to phagocytosis

molecular sieve

LPS - has important role in inflammation and infections - triggers an immune response which may be protective or pathogenic if uncontrolled

Question 15

what is the function of pili?

Answer 15

common pili = they adhere to things

conjugative pili = plasmid transfer- allow transfer of genetic information

Question 16

what is the function of spores?

Answer 16

gram- poistive bacteria can form spores which provide protection from adverse conditions

they are dormant cells but when introduced into a wound site they can germinate and cause infection

*ex. C. Dif

Question 17

can gram-negative bacteria form spores?

Answer 17

no

Question 18

Why are spores dangerous?

Answer 18

they can germinate and transmit disease

they are resistant to heat, drying, radiation, freezing, toxic chemicals, antibiotics,

must have proper autoclaving to kill a spore

Question 19

what is the purpose of a capsule/slime layer?

Answer 19

capsules = tightly associated

slime = loosely associated

both are polysaccharide or protein layers that surroudn many baterial cells

they provide protection from phagocytosis and antibiotics and play a role in bacterial adherence

Question 20

what is the role of biofilms?

Answer 20

they form when bacteria adhere to surfaces and excrete slimy glue-like substances which anchor the cells and allow them to form a community

Question 21

why do biofilm infections persist?

Answer 21

because the cells in a biofilm are protected from the immune response

antibiotics cannot penetrate biofilm well and therefore cannot reach cells

enzymes in teh biofilm matrix may destroy antibiotics

biofilm cells have altered metabolism slowly dividing cells may not be as susceptable to antibiotics

Question 22

describe the phases of growth in a bacterial culture

Answer 22

1) lag phase = adaptation
2) logarithmic phase = cells multiply at the maximum rate
3) stationary phase = lack of nutrients and buildup of toxic metabolic intermediates means multiplication is balanced by cell death
4) phase of decline

Question 23

why is the growth phase of a bacteria clinically relevant?

Answer 23

becuase infections may involve bacteria in different stages, some antibiotics work better on rapidly growing cells, but not cells in a plateau

Question 24

where do clinically relevant bacteria obtain energy?

Answer 24

it is derived from teh enzymatic breakdown of organic substrates ( carbs, lipids, proteins) - in a process called catabolism

energy generated from catabolism is used to synthesise cellular consituents in a process called anabolism

Question 25

in obligate anaerobes, what is the final electron acceptor in anaerobic respiration?

Answer 25

They cannot use oxygen as the terminal acceptor because the superoxides generated would be toxic if not detoxified by the superoxide dismutase which they lack.